1. Field of the Invention
The present invention relates to a radio communication system, and more particularly to the collection of measured values of reception statuses for the maintenance and optimization of a radio communication system.
2. Description of the Related Art
At present, efforts are being made to lower charges to be paid by subscribers to radio communication systems such as cellular phone systems, PHS, public radio LAN systems, etc. One of the efforts is to lower the operating costs of radio communication systems as much as possible. It is a large task for communication service providers to make less costly adjustments for the maintenance and optimization of radio communication systems.
The adjustments for the maintenance and optimization of radio communication systems include maintenance and adjustment activities that are performed to operate the radio communication systems stably without system failures over a long period of time. Items that need to be adjusted include, for example, the transmission power level of a radio base station and the tilt angle of an antenna.
The maintenance and adjustment of a radio communication system are generally performed based on an evaluation or examination process which employs a radio network design simulator. In order to increase the accuracy of a simulation, information about reception statuses that are measured in service areas (hereinafter referred to as “coverages”) of the radio communication system and information about positions where measured values are obtained are input to the design simulator.
In a CDMA system, for example, items of reception status information include the received signal quality and received signal intensity of a common pilot channel. These items of reception status information are useful items indispensable for system maintenance and adjustments because they serve as indexes for determining whether the services of the radio communication system are available to mobile radio terminals in the measured position or not.
Heretofore, it has been customary for a dedicated measuring vehicle or a dedicated measuring team to measure reception status information. FIG. 1 of the accompanying drawings is illustrative of a conventional process of collecting reception status information from a radio communication system. According to the conventional process, as shown in FIG. 1, coverages of the radio communication system in which radio base stations 91, 92, 93 are connected to network 90 are visited by members of measuring teams with reception status measuring vehicles 94. At each measuring spot, one reception status measuring vehicle 94 measures reception status information in the corresponding coverage. The measured reception status information is recorded in association with the positional information that is measured by position measuring device 94a on reception status measuring vehicle 94.
Using the measured reception status information, the communication service provider performs maintenance and adjustments of the radio communication system to operate the radio communication system stably without fail.
According to another conventional process of collecting reception status information, the general mobile radio terminal owned by a user is used to measure reception status information, and the measured reception status information is collected from the mobile radio terminal (see, for example, JP-2002-152104-A). According to this conventional process, reception status information can quickly and easily be collected without the need for the reception status measuring vehicle shown in FIG. 1.
The above conventional processes suffer the following problems:
The process of measuring reception status information using reception status measuring vehicles 94 shown in FIG. 1 needs a measuring team of members including a vehicle driver, a navigator, and a measuring person for driving each reception status measuring vehicle 94 and making measurements at desired spots. Expenses required to purchase and maintain the measuring vehicles and personnel expenses required to collect reception status information are large and present an obstacle to efforts to lower the operating cost of the radio communication system. The conventional process shown in FIG. 1 takes a lot of time to collect reception status information because all the coverages of the radio communication system need to be visited by a limited number of reception status measuring vehicles.
Reception status information in the coverages may be measured by many measuring teams without reception status measuring vehicles 94. However, such a modification requires increased labor costs though reception status measuring vehicles 94 are dispensed with.
In a CDMA radio communication system, when users are connected to the system, the load on the radio communication system, i.e., an interference quantity, changes, and hence coverages of the radio communication system vary with time. In order to keep stable coverages while the number of users is being progressively grown to turn the system into a mature one, it is necessary to repeatedly collect reception status information periodically. Consequently, the CDMA radio communication system requires a much greater cost for collecting reception status information than other systems because reception status measuring vehicles need to travel repeatedly periodically for collecting reception status information.
Another problem of the CDMA radio communication system is that while reception status information is being measured by reception status measuring vehicles as they travel through coverages, the user status in the measured areas may change.
According to the process of collecting reception status information with the general mobile radio terminals owned by users as disclosed in JP-2002-152104-A, reception status information can be collected at a low cost because no reception status measuring vehicles and no measuring teams of various members are required. Since the coverages of the radio communication system are not visited by reception status measuring vehicles, but reception status information is measured by the mobile radio terminals owned by general users, a large amount of reception status information can be collected in a short period of time.
In the CDMA radio communication system, however, the reception status changes for various reasons, and changes in the reception status affect the operation of the radio communication system in various ways. For example, the reception status may change either with time or as the system load changes due to a user access congestion. Changes in the reception status may cause a change in the frequency of forced communication shutdowns from the network or a change in the frequency of handover failures.
The process disclosed in JP-2002-152104-A serves to collect only the relationship between reception status information and positional information, but fails to appropriately recognize causes of changes in the reception status and phenomena brought about by changes in the reception status.